The present invention relates to a control valve, and more particularly, to a control valve for a variable displacement compressor, such as commonly used in air conditioning systems.
FIG. 8 schematically depicts an air conditioning system, such as that used in an automobile to provide passengers a comfortable atmosphere. Air conditioning systems typically include a compressor 100, a condenser 102, an expansion device 104, and an evaporator 106 fluidly connected together by tubes or hoses 108 in which refrigerant flows. In order to condition the air before it is released to the passenger compartment, heat is removed from the air by passing the air through the evaporator 106. This causes the refrigerant to boil and form a gas, which travels from the evaporator 106 to the compressor 100. The compressor 100 serves as a pump for circulating the refrigerant through the entire system. In addition, the compressor 100 may increase the temperature and pressure of the refrigerant.
Vehicle air conditioning systems commonly use variable displacement compressors, which allow the adjustment of the refrigerant pumping capacity in response to the air conditioning load. The compressor 100 comprises three main chambers, which include a suction chamber 110, a crankcase chamber 112, and a discharge chamber 114 with a valve plate 116 separating the three chambers. This valve plate 116 contains ports fluidly coupling the suction chamber 110 to other areas of the compressor 100.
Refrigerant flowing from the evaporator 106 enters the compressor 100 through the suction chamber 110 located in the rear head 118 of the compressor 100. The refrigerant flows into the suction chamber 110 into a cylinder 122 through a port 120 where pistons 124 compress the refrigerant. The compressed refrigerant exits through discharge port 126 into the discharge chamber 128 coupled to the condenser 102 by a tube or hose 108. The pressure of the refrigerant in the discharge chamber 114 always exceeds both the pressure of the refrigerant in the suction chamber 110 as well as the crankcase chamber 112.
The pumping capacity of the pistons 124 may be adjusted by changing the inclination angle xcex8 of a swashplate 130 relative to the compressor shaft 132. The pumping capacity corresponds to the stroke length of the piston 124. A larger stroke length corresponds to a higher pumping capacity and a higher pressure in the discharge chamber 114. Similarly, a lessening stroke length corresponds to a decreased pumping capacity and a lower pressure in the discharge chamber 114. The inclination angle xcex8 of the swashplate 130 relates directly to the piston 124 stroke length.
The swashplate 130 is located in the crankcase chamber 112 and is connected by pivot 134 to the compressor shaft 132 and the pistons 124. The angle formed between the connection point of the swashplate 130 and the rotation of the swashplate 130 represents the inclination angle xcex8. The rotational movement of the compressor shaft 132 rotates the swashplate 130 causing the pistons 124 to reciprocate in their cylinders. 122. The compressor shaft 132 moves responsive to the vehicle engine via a pulley 136 with the compressor shaft 132 being mounted on radial bearings 138 and shoes 140, which allows the swashplate 130 to rotate.
The crankcase chamber 112 contains refrigerant leaked by the pistons 124. Variable displacement of the compressor 100 is obtained by varying the crankcase chamber 112 pressure Pc relative to the suction chamber 110 pressure Ps. Changing the pressure differential (Pcxe2x88x92Ps) between the crankcase chamber 112 and the suction chamber 110 causes the inclination angle xcex8 of the swashplate 130 to vary, which regulates the pumping capacity of the pistons 124.
A small pressure differential (Pcxe2x88x92Ps) corresponds to an increased inclination angle xcex8. When the inclination angle xcex8 is at its maximum, the pistons 124 reciprocate at the maximum stroke thus highest compression. At this point, the air conditioning system is at its highest cooling capacity. In contrast, an increasing pressure differential (Pcxe2x88x92Ps) corresponds to a decreasing inclination angle xcex8. Decreasing the inclination angle xcex8 causes the pistons 124 to de-stroke resulting in lower compression. At this point, the air conditioning system is at its lowest cooling capacity.
For example, if the pressure differential Pcxe2x88x92Ps is low, such as 5-15 kPa, the compressor operates at maximum stroke with the swashplate 130 at its maximum inclination angle xcex8. In contrast, if the pressure differential Pcxe2x88x92Ps is high, such as 100-150 kPa, the compressor operates at minimum stroke with the swashplate 130 at its minimum inclination angle xcex8. At this point, the swashplate 130 is nearly perpendicular to the compressor shaft 130. A de-stroke spring 131 in FIG. 8 is provided to force the swashplate 130 to this position when cooling capacity is not needed.
Reference is made to U.S. Pat. No. 6,146,106 illustrating a control valve consistent with the prior art. FIG. 9 schematically illustrates the control valve 144 of the ""106 patent which may be used with the compressor schematically illustrated in FIG. 8. The variable displacement compressor 100 uses a control valve 144 to regulate the pressure differential (Pcxe2x88x92Ps). The suction chamber 110 pressure Ps changes as certain parameters in the car change, such as compressor speed. This has a direct effect on the pressure differential (Pcxe2x88x92Ps). The control valve 144 adjusts the pressure Pc in the crankcase chamber 112 relative to the pressure Ps in the suction chamber 110 in order to reach an equilibrium point. The equilibrium point is the set pressure differential (Pcxe2x88x92Ps) value of the control valve. By maintaining a constant pressure differential (equilibrium point), the cooling air entering the passenger compartment stays relatively constant regardless of changing parameters.
The control valve 144 regulates the flow of refrigerant from the discharge chamber 114 having a discharge chamber pressure Pd to the crankcase chamber 112 relative to the pressure of the refrigerant in the suction chamber 110. The control valve 144 contains a bellows 146, which compresses or expands as a result of an increase or decrease, respectively, of the fluid in the suction chamber 110. When there is a high pressure differential Pcxe2x88x92Ps, the control valve 144 allows more refrigerant to flow from the discharge chamber 114 into the crankcase chamber 112 than can escape to the suction chamber 110 through flow passage 148. The flow passage 148 is sized so that the amount of flow from crankcase chamber 112 to suction chamber 110 is less than the flow from the discharge chamber 114 to the crankcase chamber 112. As a result, the crankcase chamber pressure Pc increases, causing the compressor 100 to de-stroke. When the compressor 100 de-strokes, the suction chamber pressure Ps increases as a result of reduced refrigerant flow out of the compressor 100. The bellows 146 of the control valve 144 responds accordingly, reducing the flow into the crankcase chamber 112 until equilibrium is reached.
The bellow 146 connects to a poppet 150 or other type of member for regulating the flow from the discharge chamber 114 to the crankcase chamber 112. When the compressor 100 begins to de-stroke as the result of a high-pressure differential, the suction chamber 110 pressure increases. The fluid from the suction chamber 110 acts on the exterior of the bellows 146. An increasing suction chamber 110 pressure causes the bellows 146 to decrease in length. This moves the poppet 150 in a direction to reduce the flow from the discharge chamber 114 to the crankcase chamber 112 until the poppet 150 rests at the equilibrium point. Traditionally, the equilibrium point had a fixed setting, i.e. a set pressure differential between the crankcase chamber 112 and the suction chamber 110.
With the development of improved air conditioning systems and an increased emphasis on fuel economy, it was desired to vary the equilibrium point for a closer matching of compressor capacity to load. Solenoid-actuated control valves provide one means for varying the equilibrium point. The solenoid-actuator 152 connects to the poppet 150, which regulates fluid flow between the discharge and crankcase chamber 114, 112. As such, the solenoid actuator 152 may vary the fluid flow regardless of the pressure from the suction chamber 110. This in turn varies the equilibrium point. An electrical controller 154 connects to the solenoid for varying the amount of current supplied to the solenoid. The amount of supplied current may be set in response to various parameters, such as engine speed, vehicle speed, cabin air temperature, etc. This in turn moves the poppet 150 to a different equilibrium point.
The resultant design incorporated a mechanical bellow control valve with an electrical solenoid-actuator. This design, however, presents certain concerns. Compressors in vehicles must operate in a wide range of conditions. These conditions range from extreme heat to extreme cold. Moreover, compressors experience significant amounts of vibration from the road, vibration of the engine, etc. As a result, the bellows undergoes significant amounts of wear and tear, which reduces the bellows"" useful life. As the bellows are relatively long, the vibrations cause the bellows to vibrate and contact the internal surfaces of the control valve. Over time, the bellows have been observed to break down and lose their resiliency resulting in a less efficient air conditioning system. Once a bellows fails, typically the complete control valve must be replaced in order for the air conditioning system to work properly. However, bellows require a significant manufacturing process, increasing their replacement cost.
Accordingly, a need exists to increase the useful life of a vehicle air conditioning system, and for a control valve that will better resist the hostile environment conditions experienced in a vehicle compressor.
These and other needs are met by the present invention, which provides a variable displacement compressor having a suction chamber, a crankcase chamber, and a discharge chamber. The crankcase chamber and discharge chamber are fluidly coupled by a valve for regulating the flow therebetween as a function of pressure in the suction chamber. The valve comprises a valve housing having a chamber fluidly coupled to the suction chamber, the crankcase chamber, and the discharge chamber. The fluid flow regulation member is disposed in the chamber and is configured to regulate fluid flow between the crankcase chamber and the discharge chamber. A diaphragm is disposed substantially perpendicular to a longitudinal axis of the chamber and acts on the fluid flow regulation member as a function of the pressure in the suction chamber, the amount of longitudinal deflection of the diaphragm being responsive to the pressure in the suction chamber.
The control valve may be applied to other applications requiring the regulation of flow between two chambers relative to another chamber. This control valve is fluidly coupled to chambers containing fluid of different pressures for regulating flow therebetween. The control valve comprises a valve housing having a chamber fluidly coupled to a first chamber, a second chamber, and a third chamber. A fluid flow regulation member is disposed in the chamber and is configured to regulate fluid flow between the second chamber and the third chamber. A diaphragm disposed substantially perpendicular to a longitudinal axis of the chamber in which longitudinal deflection of diaphragm is representative of the pressure in the first chamber.
The deflection of the diaphragm discussed above acts on the fluid flow regulation member. The diaphragm has an outer perimeter shape substantially corresponding to the shape of the chamber perpendicular to the longitudinal axis. The diaphragm is configured to deflect in a first axial direction as a function of increasing force acting on the diaphragm and deflect in a second axial direction as a function of decreasing force acting on the diaphragm. In contrast, embodiments of the invention, the diaphragm comprises an undulation having at least one ridge and at least one groove. This undulation of the diaphragm compresses or expands along the axis perpendicular to the longitudinal axis of the chamber with the longitudinal deflection of the diaphragm. The outer periphery of the diaphragm is hermetically sealed to the inner wall of the chamber creating a volume between the diaphragm and an end of the chamber. A vacuum exists in this volume.